Rent in San Diego is getting more expensive, unless you want a studio apartment.

The average rent in San Diego County is now $1,311 per month, a 2 percent jump over this time last year, a study released this week from the San Diego County Apartment Association says. But more people are now moving into one-bedroom units, while a lack of demand for studios since the Great Recession has caused those rental rates to drop 17 percent.

Rents rose dramatically during downturn, when foreclosures were mounting and people moved into apartments. The biggest annual jump came in fall 2010, when the average rent rose 12.7 percent from a year earlier to $1,341 per month. In 2010, rent for studio apartments hit $1,040 per month.

"If you lost your job but you needed a place to stay you'd go with the lowest possible thing you could get," said Alan Gin, economist at the University of San Diego.

But things have changed since the recession, and people apparently don't want single-rooms anymore. Now, studios are going for an average $861 per month. That could be due to an improving housing market and falling unemployment rate.

“The rental market remains strong throughout San Diego County,” said a statement from Alan Pentico, the apartment association's director. “Rents are up slightly and you can connect that to our improving local economy."

Overall, the vacancy rate in San Diego County is 4.1 percent, a decrease from the 4.5 percent it was at this time last year.

Developers each year since 2007 have responded to the higher demand for rental units by obtaining more permits to build apartments than single-family homes, Gin said. That's opposite what happened from 2000 to 2006, when single family home building outnumbered new apartments. It's helped increase supply and kept rents from rising dramatically despite low vacancy.

Pentico noted that more people are moving into one-bedroom apartments and fewer families are taking multi-bedroom apartments. Gin said that could be because people in their 20s are finally making enough money to move out of their parents' homes.

Here's how the apartments break down by size, compared to the Great Recession peak in Fall 2010: